Coiled coil (designation for a double-wound screw) refers to a special protein structure motif, a so-called double helix. Simplified, this designates a helix, which in turn is formed into another helix with a larger radius. A coiled coil structure is therefore at least 2 single helices.
One of the most common coiled coil structures is the so-called bZIP domain (also known as leucine zipper). Coiled coil motifs are found in many proteins, for example in transcription factors or in proteins involved in vesicle transport. It is assumed that they still often have a spacer function. In some proteins, they also contribute to dimer formation.